| … | |
… | |
| 1922 | |
1922 | |
| 1923 | |
1923 | |
| 1924 | =head2 C<ev_stat> - did the file attributes just change? |
1924 | =head2 C<ev_stat> - did the file attributes just change? |
| 1925 | |
1925 | |
| 1926 | This watches a file system path for attribute changes. That is, it calls |
1926 | This watches a file system path for attribute changes. That is, it calls |
| 1927 | C<stat> regularly (or when the OS says it changed) and sees if it changed |
1927 | C<stat> on that path in regular intervals (or when the OS says it changed) |
| 1928 | compared to the last time, invoking the callback if it did. |
1928 | and sees if it changed compared to the last time, invoking the callback if |
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1929 | it did. |
| 1929 | |
1930 | |
| 1930 | The path does not need to exist: changing from "path exists" to "path does |
1931 | The path does not need to exist: changing from "path exists" to "path does |
| 1931 | not exist" is a status change like any other. The condition "path does |
1932 | not exist" is a status change like any other. The condition "path does |
| 1932 | not exist" is signified by the C<st_nlink> field being zero (which is |
1933 | not exist" is signified by the C<st_nlink> field being zero (which is |
| 1933 | otherwise always forced to be at least one) and all the other fields of |
1934 | otherwise always forced to be at least one) and all the other fields of |
| 1934 | the stat buffer having unspecified contents. |
1935 | the stat buffer having unspecified contents. |
| 1935 | |
1936 | |
| 1936 | The path I<should> be absolute and I<must not> end in a slash. If it is |
1937 | The path I<must not> end in a slash or contain special components such as |
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|
1938 | C<.> or C<..>. The path I<should> be absolute: If it is relative and |
| 1937 | relative and your working directory changes, the behaviour is undefined. |
1939 | your working directory changes, then the behaviour is undefined. |
| 1938 | |
1940 | |
| 1939 | Since there is no standard kernel interface to do this, the portable |
1941 | Since there is no portable change notification interface available, the |
| 1940 | implementation simply calls C<stat (2)> regularly on the path to see if |
1942 | portable implementation simply calls C<stat(2)> regularly on the path |
| 1941 | it changed somehow. You can specify a recommended polling interval for |
1943 | to see if it changed somehow. You can specify a recommended polling |
| 1942 | this case. If you specify a polling interval of C<0> (highly recommended!) |
1944 | interval for this case. If you specify a polling interval of C<0> (highly |
| 1943 | then a I<suitable, unspecified default> value will be used (which |
1945 | recommended!) then a I<suitable, unspecified default> value will be used |
| 1944 | you can expect to be around five seconds, although this might change |
1946 | (which you can expect to be around five seconds, although this might |
| 1945 | dynamically). Libev will also impose a minimum interval which is currently |
1947 | change dynamically). Libev will also impose a minimum interval which is |
| 1946 | around C<0.1>, but thats usually overkill. |
1948 | currently around C<0.1>, but thats usually overkill. |
| 1947 | |
1949 | |
| 1948 | This watcher type is not meant for massive numbers of stat watchers, |
1950 | This watcher type is not meant for massive numbers of stat watchers, |
| 1949 | as even with OS-supported change notifications, this can be |
1951 | as even with OS-supported change notifications, this can be |
| 1950 | resource-intensive. |
1952 | resource-intensive. |
| 1951 | |
1953 | |
| … | |
… | |
| 1961 | support disabled by default, you get the 32 bit version of the stat |
1963 | support disabled by default, you get the 32 bit version of the stat |
| 1962 | structure. When using the library from programs that change the ABI to |
1964 | structure. When using the library from programs that change the ABI to |
| 1963 | use 64 bit file offsets the programs will fail. In that case you have to |
1965 | use 64 bit file offsets the programs will fail. In that case you have to |
| 1964 | compile libev with the same flags to get binary compatibility. This is |
1966 | compile libev with the same flags to get binary compatibility. This is |
| 1965 | obviously the case with any flags that change the ABI, but the problem is |
1967 | obviously the case with any flags that change the ABI, but the problem is |
| 1966 | most noticeably disabled with ev_stat and large file support. |
1968 | most noticeably displayed with ev_stat and large file support. |
| 1967 | |
1969 | |
| 1968 | The solution for this is to lobby your distribution maker to make large |
1970 | The solution for this is to lobby your distribution maker to make large |
| 1969 | file interfaces available by default (as e.g. FreeBSD does) and not |
1971 | file interfaces available by default (as e.g. FreeBSD does) and not |
| 1970 | optional. Libev cannot simply switch on large file support because it has |
1972 | optional. Libev cannot simply switch on large file support because it has |
| 1971 | to exchange stat structures with application programs compiled using the |
1973 | to exchange stat structures with application programs compiled using the |
| … | |
… | |
| 1990 | descriptor open on the object at all times, and detecting renames, unlinks |
1992 | descriptor open on the object at all times, and detecting renames, unlinks |
| 1991 | etc. is difficult. |
1993 | etc. is difficult. |
| 1992 | |
1994 | |
| 1993 | =head3 The special problem of stat time resolution |
1995 | =head3 The special problem of stat time resolution |
| 1994 | |
1996 | |
| 1995 | The C<stat ()> system call only supports full-second resolution portably, and |
1997 | The C<stat ()> system call only supports full-second resolution portably, |
| 1996 | even on systems where the resolution is higher, most file systems still |
1998 | and even on systems where the resolution is higher, most file systems |
| 1997 | only support whole seconds. |
1999 | still only support whole seconds. |
| 1998 | |
2000 | |
| 1999 | That means that, if the time is the only thing that changes, you can |
2001 | That means that, if the time is the only thing that changes, you can |
| 2000 | easily miss updates: on the first update, C<ev_stat> detects a change and |
2002 | easily miss updates: on the first update, C<ev_stat> detects a change and |
| 2001 | calls your callback, which does something. When there is another update |
2003 | calls your callback, which does something. When there is another update |
| 2002 | within the same second, C<ev_stat> will be unable to detect unless the |
2004 | within the same second, C<ev_stat> will be unable to detect unless the |
